Here’s the core of my program, that configuration is everything you need:
.. cmd:= 'OHMF 1000;APER 1;OCOMP ON;TRIG HOLD;DELAY 0.1;'; // for 1kOhm\
else cmd:= 'OHMF 10000;APER 1;OCOMP ON;TRIG HOLD;DELAY 1;'; // OCOMP
requires settling time, 1s for VHP for 0.1ppm\
sendstr(HP3458);
for N_Samp:= 1 to 16 do begin\
..\
TRIGHP34401;\
cmd:= 'TRIG SGL;’;\
sendstr(HP3458);\
Temperature:= NTC_2k8(fetch(HP34401))-273.16;\
..\
Resistance:= fetch(HP3458); // ASCII read\
..\
Resistance_25:= Resistance \* (1 + (25.0-Temperature)\*
TC_Factor);\
Do_Statistics;\
end;\
cmd:= 'TRIG AUTO;';\
sendstr(HP3458);\
Goto_Local(HP34401);\
Goto_Local(HP3458);\
EndCEC;\
..
You are using AZERO ONCE, that is not necessary at all with OCOMP as the DMM in
this mode substracts e.m.f. and offsets anyhow.
Then you are using TARM, I think, that’s also not necessary, maybe even
counter productive.
I have found a comment in my DCV acquisition program, that TRIG SGL and TARM
creates many ppm of offset, so I skipped that, and let the DMM running free on
TRIG AUTO. \
For Ohm, TRIG SGL seems to work for my FW 9, maybe that is still a problem on
your old FW version.
Background is, that in the DCV specification there is a footnote, that the
first sample might have 1ppm deviation, and that seems to apply for halted
(armed & triggered) measurements in particular.
So maybe you find some further hints to eliminate your measurement problem.
Frank
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